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The importance of a bond

A method to estimate the strength of a carbon-carbon double bond
The importance of a bond


Oeiras, 01.06.09

Being able to accurately measure the strength of chemical bonds is one of the most important goals in chemistry.  Some bond strengths are particularly difficult to measure, such as the π-bond strength in a C=C double bond.  This might seem nitpicking, but only at first sight (pun intended). A paper recently published in the Journal of Physical Chemistry A and involving ITQB  researchers, describes an experimental alternative to the current methods of π-bond strength estimation, illustrated by the addition of tert-butoxyl radical to the highly strained norbornadiene molecule.

The proposed experimental method is based on the study by time-resolved photoacoustic calorimetry (PAC) of the reaction between tert-butoxyl radical and norbornadiene.  PAC is a calorimetric technique that measures the heat involved in very fast reactions (such as that one), by allowing researchers to “listen” to them (see more information on PAC).

The tert-butoxyl radical is widely used in PAC studies to measure the strength of chemical bonds, because of its marked tendency to abstract hydrogens from other molecules, cleaving X–H bonds (X = C, N, O…) in the process (the strength of the bond is related to the heat of this reaction).

In conclusion, it is the unusual norbornadiene structure that is responsible for the atypical behavior of tert-butoxyl radical, thus providing a model reaction that can be used to measure the strength of the π-bond. 


 A bond at first sight


Original Paper:

J. Phys. Chem. A, Article ASAP, DOI: 10.1021/jp900089t

Energetics of tert-Butoxyl Addition Reaction to Norbornadiene.  A Method to Estimate the π-Bond Strength of a Carbon-Carbon Double Bond

Paulo M. Nunes, Sílvia G. Estácio, Gustavo T. Lopes, Filipe Agapito, Rui C. Santos, Benedito J. Costa Cabral, Rui M. Borges dos Santos (ITQB), and José A. Martinho Simões (ITQB)



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